The present invention relates to an apparatus for welding the end plugs on the fuel rods filled with nuclear fuel pellets.
In general, each fuel rod for use in nuclear reactors contains fuel in the form of pellets.
In a conventional method for producing such fuel rods, a given quantity of pellets are inserted into a closed-end fuel rod tube and, to retain the pellets in place in the rod, a spring in inserted together with the end plug, and the fuel rod is sealed by welding the end plug to the rod tube (fuel rod). To ensure the contact between the end plug and the fuel rod end against the force of the spring, the conventional practice has been to press fit the end plug into the tube to provide contacts, and then to weld the end plug to the rod.
Because of such a configuration of the fuel rod, however, welding is carried out while holding the positions of the fuel rod and the end plug fixed to prevent loosening of the plug and obtain uniform welding around the rod. However, it was difficult to achieve uniform welding with such a welding method, because of the variations in the state of contact between the rod and the end plug during welding, caused by thermal distortions of the fuel rod, i.e. changing stress conditions at the weld due to the axial expansion and contraction in the fuel rod. Achieving a high degree of welding precision by such conventional method required a substantial welding expertise.